1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to a method of sensing a laundry amount in a washing machine.
2. Discussion of the Related Art
Generally, a washing machine is an apparatus for washing laundry by performing washing, rinsing, and dewatering steps according to a predetermined algorithm, i.e., a selected wash course, whereby water is supplied to an appropriate water level, which is determined in part by sensing an amount of laundry placed in the washing machine before initiating a wash command and setting a water level accordingly. The laundry amount is sensed using a voltage sensing unit, which is configured with a motor and clutched pulley assembly for the drive of a pulsator within a tub and essentially consists of a microprocessor receiving a voltage signal generated by an opposing pair of rotating magnets and a fixed coil disposed with respect to the magnets. That is, upon input of a wash command, the pulsator is rotated for a predetermined time to generate movement in the laundry. Simultaneously, the rotating magnets of the voltage sensing unit generate a series of pulses by disrupting the flux field of the coil. Notably, the effected rotational speed of the pulsator varies according to the amount of laundry in the tub, to produce a varying number of pulses, i.e., a pulse count, for input to the microcomputer.
Referring to FIG. 1, a washing machine according to a related art is comprised of a key input unit 1 for inputting a user command; a voltage sensing unit 2 for monitoring a voltage and providing a voltage signal output in the form of a series of voltage pulses as described above; a controller 3, e.g., a microcomputer, for receiving the voltage signal and outputting a control signal to control the washing machine according to the received voltage signal; a load driver 4 for driving various loads (not shown) such as a motor, valves, and the like according to the control signal; and a display 5 for displaying an operational status of the washing machine. Typically, laundry is placed in the washing machine, the washing machine is turned on, and a wash command is input via the key input unit 1, whereupon the controller 3 outputs a wash command control signal to the load driver 4 to rotate the pulsator for a predetermined time.
As a result, a predetermined number of pulses is generated in proportion to the amount of laundry placed in the tub. The pulses are input to the controller 3, which counts the pulses to determine a pulse count falling into one of a plurality of ranges, i.e., 30˜52, 53˜77, 78˜98, 99˜119, and 120 or more, designated as high, medium, low, small, and minimum, respectively. Accordingly, a low pulse count, meaning a slow pulsator rotation due to a large amount of laundry (load), results in the setting of a high water level; and a high pulse count, meaning a fast pulsator rotation due to a small laundry load, results in the setting of a low water level. The controller 3 then determines the water level setting by comparing the sensed pulse count to an internally stored table, comprised of a plurality of predetermined water level values according to corresponding pulse counts as above, and outputs a control signal to the load driver 4 for performing a washing step in accordance with a washing machine control method such as that shown in FIG. 2.
Referring to FIG. 2, illustrating a washing machine control method according to a related art, a dry laundry amount in a tub is sensed (S1) to determine a corresponding water level (S2), and water is supplied to the tub (S3) until the water level is reached (S4). Thereafter, the laundry amount is sensed again, i.e., a wet laundry amount (S5), to determine a wash pattern (S6). Finally, washing is performed according to the wash pattern (S7).
In the above process, it is assumed that laundry is placed in the tub before initiating the dry laundry amount sensing step, e.g., by manipulation of a wash command key of the key input unit 1. If, however, manipulation of the wash command key occurs before the laundry is placed in the tub, an empty washing machine is activated, so that the laundry amount is sensed without any laundry load (an empty washing machine), which results in a maximum pulse count, i.e., greater than 120, and the corresponding minimum water level setting. At the same time, it should be appreciated that at least a portion of the laundry may be placed in the tub after the wash command key manipulation. In doing so, the wash step is performed based on an inaccurate sensing of the laundry amount, which degrades washing performance. That is, the water level according to the sensed laundry amount is already set when the wash pattern is determined.